Persons engaged in maintenance and repair of chimneys and other pipes and ducts have long used shafts, also called poles, comprised of coupled-together shaft segments, for a variety of applications. Shafts are provided in short sections to enable easy transport between jobs.
In one use, a mechanic uses tool such as a brush or a lifting device of the kind described in U.S. Pat. No. 9,027,977. The tool is attached to the end of a shaft and lowered into the chimney interior, which may be straight or crooked. In another use, a mechanic puts a flail-like cleaning tool on the shaft and inserts it into the lower part of a chimney or stovepipe, using a power tool to rotate the tool as it moves upwardly. In another use, a mechanic puts a flail or brush on the end of a shaft and runs it along an air duct or pipe, some of which have rather small diameters compared to a typical chimney, to remove deposits.
The prior art uses require good fit and stiffness of a shaft coupler. As a result, the shaft, and therefore, the coupler of the shaft segments, can be subjected to substantial torsional and longitudinal forces. Insofar as practical, it is desirable that a shaft comprised of segments behave as if it was a unitary structure.
Particularly during the course of chimney work it is common that soot deposits, masonry particulate, and other debris are agitated within the chimney and thus will contact any coupling. The coupling may also be subjected to water wetting during handling and use. Similar dirt and debris problems can be present during other uses.
Various kinds of couplers have been used to interconnect shaft pieces in the past. A familiar kind of prior art coupler comprises a male part and a female part: the male part has a spring loaded, radially-moving plunger (also called a button) which engages a hole or cutout in a mating female part, thereby to lock the two parts together. Generally, there has been a tendency for the plungers of prior art couplers to stick when being engaged, or insufficiently to resist unwanted disengagement, especially as wear of the coupler occurs over time.
U.S. Pat. No. 6,688,800 of Kresge describes a coupler which comprises a single snap-like plunger lock. UK Pat. 2500288 and UK Patent Application GB2509004, both of Russell, describe other couplers having single buttons.
A good coupler must be able to function well in engage and disengage in dirty environments, and resist inadvertent disengagement. Engagement and disengagement of a coupler—even when small in diameter, will desirably be easy, including for a person wearing gloves. A coupler should be strong in resisting forces in longitudinal shaft directions, and in torsional directions. A desirable coupler will have a plunger which will not twist or jamb, and which will function properly even if it becomes worn. Generally, it is hard, when a coupler is small in diameter to make a coupler which is strong, easy to engage and disengage, and durable. As described below, the present invention lends itself to small size coupler.